The present invention relates generally to fluid seals and methods, and more particularly, to assembled or unitized seals and methods of assembling them by insert molding and bonding so as to insure that they may be protected against damage after manufacture and during shipment and installation.
Historically, oil seals and other fluid seals, such as those used to retain grease or the like within sealed cavities, were made from primitive materials such as leather or the like. With the advent of synthetic rubber, particularly oil resistant rubbers and the like, great improvements in the design of seals were made. Rubber is very advantageously used as a primary seal material because it is relatively rugged, is resilient for a snug fit over an associated shaft, and because it retains its elasticity over a long period of time.
More recently, other synthetic materials which are themselves not ideal for seal application have been able to be made in special forms, or to be combined with other materials to provide good sealing performance. Included among these are materials such as polymers of tetrafluoroethylene or the like, which are characterized by a very lubricous surface, and which are able to perform a sealing function if properly constructed and arranged. An advantage of these synthetic materials is that they resist rapid wear, they perform very well in relatively dry environments, such as those wherein all or part of the seal is not literally immersed in oil, they perform well in some dusty environments, and they are also advantageous wherein the sealed medium itself is not particularly lubricous.
However, fluorocarbon materials do not wear well when mated with rough surfaces, and synthetic rubbers do not perform well in dry sealing environments. Fluorocarbon materials are very susceptible to nicking or other surface damage which compromises their ability to seal effectively.
A seal failure is very critical in modern sealed mechanisms wherein the seal itself may cost relatively little, but wherein the value of the sealed mechanism and hence the damage potential in the event of seal failure, is large, or wherein the seal is inaccessibly located, as is common with many compact and complex machines of today. Still further, there is the problem of materials which are resistent to wear and nicking but which themselves are relatively hard and therefore tend to cut grooves or the like in associated shafts, causing a problem with eventual replacement.
Under these circumstances, there has been an increasing need for so-called unitized seals, that is, seals wherein both the sealed-against or wear sleeve element is combined with the seal element itself into a single mechanism. By "unitizing" or preassembling these elements, proper dimensional installation is achieved, protection against nicking or other damage during handling is avoided, prelubrication, if desired, may be insured, and correct dimensional or manufacturing tolerances may be controlled at the point at which the seal is manufactured as opposed to the point at which the other parts are manufactured or assembled.
According to the invention, improved, relatively simplified assembled or unitized seals are provided, and methods are also provided for assembling the seal so that the damage sought to be avoided during installation in the customer's manufacturing facility is able to be avoided in the seal maker's own manufacturing facility.
In view of the need for specialty assembled seals, it is an object of the invention to provide improved methods for manufacturing assembled, unitized seals having two components protectively held together for shipment and installation.
Another object of the invention is to provide a improved seal assembly which provides a seal having a unitizing element adapted to fit over one portion of a sealed mechanism and a primary seal assembly adapted to be received within or with respect to another sealed part which moves relative to the first sealed part.
A still further object of the invention is to provide a seal which includes a unitizing or locking flange made from a reduced thickness or skirt portion at the end of the wear sleeve on the unitizing element, such flange being axially offset from the seal contact band.
A still further object of the invention is to provide an assembled seal made from a casing unit, an elastomer which provides a mounting surface and a resiliency imparting element, together with a bonded fluoroelastomer ring and which is assembled protectively with a unitizing casing which includes a wear sleeve portion having one radial flange thereof forming a protective element and the other being a unitizing flange made from an end portion of the wear sleeve.
Another object of the invention is to provide a method which includes using a mandrel or the like having a tapered body portion with a skirt thereon adapted to engage an axially extending portion of the wear surface of the seal unit, and a contoured end face portion to guide the seal body into a position overlying the wear surface during assembly, removing the mandrel therefrom after positioning the seal, and then forming a unitizing flange from an axially extending skirt on the casing into a radial locating or locking assembling flange.
A still further object of the invention is to provide a seal wherein the locking or unitizing flange is dimensioned so as to permit oil or other lubricant to contact the seal formed on the seal band of the primary seal lip, and yet to prevent free axial removal of the seal lip from the wear sleeve. Another object is to provide a unitizing construction and method which operates successfully both with seals having all-elastomeric seal bodies as well as seals having composite elastomer-fluorocarbon seal bodies.
The foregoing objects and advantages of the invention are achieved and practiced by providing a seal having a primary seal element including a casing element of annular form made from a relatively rigid material and having an at least partially elastomeric sealing lip body bonded thereto, and a single or one-piece wear sleeve and unitizing casing portion including a radial flange acting as as axially exterior protective element preventing relative axial movement of the associated primary seal in one direction, an axially extending wear sleeve portion having a cylindrical outer diameter surface facing toward and sealingly engaged with the seal band portion of the primary lip, and a second, unitizing or locking flange of reduced thickness and reduced diameter with respect to the protective flange and preventing axial removal of the primary seal unit in the other axial direction.
The invention also achieves its objects by providing a manufacturing method which includes forming the primary seal and a wear sleeve element with a protective flange and a reduced thickness skirt portion, placing a tapered mandrel skirt- engaging portion in overlying relation to the reduced diameter skirt of the wear sleeve, and sliding the primary lip portion of the primary seal unit over the tapered surface of the mandrel and into the desired position of use overlying the wear sleeve portion of the casing and thereafter utilizing a curling die to flange the skirt portion of the unitizing casing so as to provide a radially extending unitizing flange spaced apart from the radial protective flange of the wear sleeve element to lock the elements together.
The manner in which the foregoing and other objects and advantages of the invention are achieved in practice will become more clearly apparent when reference is made to the following detailed description of the preferred embodiments of the invention set forth by way of example and shown in the accompanying drawings, wherein like reference numbers indicate corresponding parts throughout.